Continuous manufacture of rayon yarns



y 1953 R. H. MCKEE 2,637,069

commuous MANUFACTURE OF RAYON YARNS Filed Sept. 23. 1948 2 SHEETS-SHEET 1 f INVENTOR.

RALPH h. M KEE BY ATTOR/VEX May 5, 1953 R. H. MCKEE CONTINUOUS MANUFACTURE OF RAYON YARNS 2 SHEETS-SHEET 2 Filed Sept 25, 1948 INVENTOR. RALPH VKEzE A Trek/v5) Patented May 5, 1953 CONTINUOUS MANUFACTURE OF RAYON YARNS Ralph E. McKee, New York, N. Y. Application September 23,1948, Serial No. 50,837

This invention relates to the manufacture of viscose rayon yarns and particularly to a method and an installation for their continuous produc tion.

A large number of continuous rayon spinning methods have been developed in the recent past, but few have attained the stage of satisfactory practicability and commercial usefulness. Those processes which have reached a certain degree of commercial application are, in general, those which are exclusively concerned with the production of the viscose filaments, their treatment with acids, washing and drying. The spinning speed is ordinarily limited to about not more than 125 feet per minute; additional treatment steps of the yarns such as stretching, desulfurising, bleaching, oiling, sizing, impregnation, for instance, with latex solutions, crimping and other chemical and physical processes are rarely or not all included in the continuous manufacturing procedure. These steps are indeed performed after the completion of the continuous manufacture of the yarns and by independent means or devices. As a consequence thereof the installation, labor and manufacturing costs are unduly increased; the expenses of equipment and repairs for the same rayon production in the hitherto known continuous plants are approximately twice as high as those required in standard bobbin and centrifugal box methods.

The great majority of the continuous rayon manufacturing processes described in the literature rely for the continuity of the work on the employment of endless belts which are supported on rollers. the rollers only effect the transport of the viscose Sometimes the belts are omitted and filaments and yarns through the manufacturing plant; their processing is generally performed after the yarns have left the roller beds.

In compliance with these objects single rollers or parallel pairs or sets of rollers have been prothrough successive treating baths or the viscose yarns are transported by rollers directly and without supports through a succession of individual processing tanks; the rollers are either separated from the treating baths or rotate partly in the same.

A stretching of the yarns between the individual treating baths has been suggested in combination with the roller installations. Moreover Claims. (Cl. 18-8) spinning equipments belong to the state of the art where series of pairs of vertically spaced parallel thread, supporting rollers are provided the rollers of the lower series being partly immersed in the treating fluids. The use of a succession of roller pairs has also been suggested for horizontal continuous rayon spinning installations; hoW- ever, the arrangement and the cooperation of these roller pairs is essentially differentiated from this invention as will appear from the following specification.

It is a primary object of this invention to provide a horizontal spinning system wherein the regeneration of the extruded filaments and the processing of the regenerated yarns is eifected by a plurality of intermediary and finishing steps during the continuous passage of the yarns through a roller bed' consisting of subsequent rollerpairs.

It is a further important object of this invention to greatly reduce the quantity and the vol ume of the liquid treating media and accordingly thesize of the vessels containing the same.

It is another object of this invention to eifect a successive contact of the treating liquids with the yarns and their successive removal from the yarns as the latter pass around each roller pair.

' It is a further object of the invention to vary the degree or intensity and time of the treatment during the passage of the yarns over each individualroller pair.

It is also an object of the invention to provide for an easy change of the traveling speed of the yarns through the installation in conformity with a'constantly proportionate feed of the viscose solution to the spinnerets.

The use of the same and unchanged equipment for the production of yarns from the finest denier up to heavy yarns as used in tire cords and staple fibers is a further important object and achievement of this invention.

Moreoventhe invention provides an easy manner of combining the filaments extruded from two or more spinnerets at any desired stage of their manufacture.

It is another object of the invention to utilize the greater portion of the roller circumference for the processing of the threads in contradistinction to hitherto disclosed spinning methods where a limited roller surface only is used for this purpose and accordingly the speed of the rollers must be reduced or excessively long treatment baths must be installed; a great strain is hereby imposed on the threads due to the liquid drag through the long treating vessels.

It is a further accomplishment of this invention to render a counter-current processing of the yarns more easily applicable, to hereby save chemicals and to reduce the volume of water and other treating liquids used in the process and of heat for those treating baths that must be kept above room temperature.

It is also an object of this invention to effect an intensive and complete impregnation of the yarns with the treating liquids during their passage through the roller bed and to constantly replace the treating liquids by a successive squeezing and loosening action applied to the filaments or yarns by the rollers.

A further object of the invention resides in the avoidance of any intermediate handling of the yarns from the moment of their extrusion until they are assembled as completely dried twisted yarns on cones and bobbins and like devices.

It is a further object of the invention to facilitate the threading of the yarns over the rollers at the commencement of the operation and to restart broken yarns.

Additional objects of this invention will .become apparent from the following detailed de" scription when considered in connection with the attached drawings.

In these drawings:

Fig. 1 is a schematical vertical sectional view of a spinning installation for use in the continuous production of viscose rayon yarns in accordance with this invention, only a fraction of the treating baths and the coordinated roller pairs are being shown;

Fig. 2 is a more detailed fragmentary side view of the installation partly in section the spinning direction being here opposite to that of Fig. 1;

Fig. 3 is a plan view corresponding to Fig. 2;

Fig. 4 illustrates schematically a difierent mode of .travel of the yarn over the roller bed;

Fig. 5 illustrates a further mode of applying the treating liquid to the lower rollers and Fig. 6 is a schematical side view of a roller pair illustrating the travel of each yarn over the rollers in the form of individual groups composed of adjacent spiral circuits.

If an elongated article such as a string, wire, rope or yarn is passed over a pair of rotating rollers whose axes are parallel, this article will pile up in consecutive layers on the rollers. But r if a pair of rollers is used of which the longitudinal axes are slightly inclined relative to each other and the article is passed .from one to the other roller, then the progress of this .article will take place in adjacent spiral circuits over the length of the roller pair. The above characterized inclined position of the two rollers of a roller pair will be denoted in the following desciption and in the claims as non-parallel.

This invention utilizes this principle for the transport and the passage of extruded viscose yarns over a horizontal succession of adjacent, vertically spaced pairs of non-parallel rollers having treating baths operatively coordinated thereto, the latter being preferably located beneath the lower rollers and in operational contact therewith. The yarns which in the customary manner are extruded from adjacent spinnerets are conducted onto the first non-parallel roller pair which is generally coordinated with a coagulation bath. The individual yarns travel over this non-parallel roller pair in the form of groups of spiral adjacent circuits. The maximum width of the groups or the maximum number of the yarn circuits of each group is limited by the mutual distance of the spinnerets and their accessories. The yarns are then conducted in the same manner over a large number of non-parallel roller pairs in conformity with the requirement of completing the regeneration, of stretching or combined stretching and shrinking of the yarns and of all those treatment steps of a chemical and mechanical nature which are considered appropriate until the yarns are dried and collected on cones or similar assembling devices. The stretching or the combined stretching and shrinking of the yarns is either effected during their passage through the coagulation and regeneration baths which are ordinarily maintained at a temperature of not less than 50 to 60 C., or this treatment is efiected during a later stage of the process in contact with steam or very hot water having a temperature of near to C. The degree of stretching used will vary from 20 per cent to as much as 100 per cent according to the type of yarn made.

In the above described manner the yarns contact the non-parallel rollers on a much greater part of their circumference than in the customary spinning installation using sets of parallel rollers or roller pairs where only less than half of the roller circumference is utilized; as a consequence thereof the rollers used for the known processes must be driven at a low speed or excessively long treating baths must be used which imposes, due to the resulting drag, a greater strain on the yarns than they can endure. With the present invention, however, speeds may be easily obtained of up to 4.00 it. per minute under avoidance of any appreciable drag. The use of one single pair of non-parallel rollers has been already suggested in the viscose spinning art, but only for the regeneration and washing of the viscose yarns and without desulfurising, bleaching or other needed treatments.

The important progress of the present invention is based on the use of a horizontal succession of non-parallel roller pairs for the complete treatment of the yarns including coagulation, regeneration, washing, stretching, stretching and shrinking, and any type of afterand accessory treatment steps of a chemical and mechanical nature, the individual treating baths being preferably coordinated to the individual roller pairs; the yarns extruded from the adjacent spinnerets are conducted over corresponding sections of each roller pair in groups consisting of several spiral circuits. The number of the spiral cir cuits within the individual yarn groups may vary between 3-8, this number depending mainly upon the mutual distance of the spinnerets. The roller of the individual pairs may be tilted either in the horizontal or in the vertical or in both directions; the purposes of this invention are generally best served if only one roller of each pair is vertically tiled relative to the other one which will remain in the customary horizontal untilted position; it is preferable to tilt the upper roller only. The inclination of the rollers is very slight. If the rollers have their axes spaced approximately one yard from each other and have a diameter of about 10" the upper roll, having about a 6 it. length, should be tilted at the one end about which will correspond to an angle of 0-18. The yarn strands will in this case progress over the roller at a distance of about A from each other and will not overlap. The yarn fed on the tilted roller runs up on the same. Change of the traveling speed does not change its position on the rollers. As

the yarn passes up on the roller it will be stretched as the distance between the rollers increases; however, this stretching action is of a minimal and inconsequential degree and its infiuence may be fully ignored; it can be entirely compensated by changing the tilting direction of the next pair of the rollers as shown in Fig. 4. Driving force may be imparted to both rollers of the individual roller pairs; however, practical experience has proven that only one and preferably the lower roller should be driven because the upper rollers are readily rotated by the pull of the yarn from the driven lower rollers. .The linear speed of the yarn canbeeasily kept at 300 it. a minute and may be run up to 400 ft. and more without undue spraying of the treating liquids. After the roller bed has been set into operation, half or even more of the roller driving mechanisms may be thrown out of connection with their drive shafts as they Will be satisfactorily driven by the pull of the traveling yarn. One master motor with its attached Variable speed reducer connected to a single main shaft driving both the viscose pumps and the gears rotating the roller bed is all that is required for the operation of this invention. Accordingly by changing the speed reducer a yarn movement may be obtained of, for instance, only 20 ft. per minute at the start of the plant operation which by a shift of the control on the reducer may be gradually increased to 100, 200 or even 400 it. if desired, without incurring a breakage of the yarns. It is true that the spiral propulsion of the threads over the rollers will require corresponding space; however, since a single row of the spinnerets cannot be placed closer than about two inches there will be no loss of usable space on the non-parallel rollers of this invention.

The length of the rollers will be mainly determined by the working reach of the plant attendants from both sides of the roller bed. A length varying between to 8 ft. will correspond to this requirement. The limit in the length of the rollers will essentially depend upon the ability of the attendants to thread the rayon yarn onto the rollers when the installation is started. A workman has an easy reach of up to about 4 ft. and that will be the determining factor for the length of the rollers.

As will be more clearly apparent from the following detailed description, the use of comparatively small quantities of treating liquids and of correspondingly small-sized vessels is a pa ticular advantage of this invention; the level of the treating liquids in the individual baths should be kept as constant as possible the lower rollers reaching with their lower faces only into these baths. If several baths of the same treating 'type, for instance, several coagulation or several washing baths are installed they may be operated in accordance with the counter-current system to reduce the costs of chemicals and the quantity of water or to save steam if the baths are kept above room temperature. The individual baths may be fed by small pumps from supply tanks situated, for instanca'beneath the same each having an overflow near the feed inlet which overflow feeds back to its supply tank. The height between the inlet and the overflow pipe will in this case determine the level of the bath liquid. Since the yarn does not dry in passing from one pair to the adjacent roller pair a complete washing or impregnation is attained during the entire movement of the yarn with replacement of the treating liquid by a new bath liquid every time the yarn passes over the lower surface of the lower roller.

This procedure is improved, as follows.

When the yarn is vertically passed between the rollers of a roller pair it has an essentially circular shape surrounded by a film of liquid. On passing over a roller, the yarn is subjected to pressure by the tension imposed thereon and its shape is changed and flattened accordingly; at the same time the liquid is largely squeezed out. Upon leaving the roller the original shape is more or less reestablished and the treating liquid is again taken up. This change of shape and movement of the treating liquids takes place every time the yarn passes repeatedly on and off the rollers of each pair; almost ideal conditions for the treatment of the yarns and particularly for their washing, regeneration and impregnation, for instance, with latex liquids are thus es-- tablished.

Since the wet yarns cling to the non-parallel rollers in a very satisfactory manner a greatly improved mode of stretching or combined stretching and shrinking of the yarns may be applied; for this purpose the roller pair receiving the incompletely regenerated yarns are rotated at a greater speed than the preceding roller pair. If, for instance, two roller pairs are provided in the regeneration bath the yarn is stretched by this speed cooperation. If two regeneration baths are used, the last being more acid than the first, an additional stretchingis imparted before the change of the yarns from cellulose xanthate to regenerated cellulose is completed. A following roller pair may then effect shrinking by a corresponding speed reduction; if a stretch of about 20 per cent has been made a shrinkage of about 2 per cent is adequate.

With the exception of the very start of the installation the entire process is carried-out automatically and with elimination of any hand handling of the yarn after the same has once been threaded onto the roller bed. For a complete treatment approximately twelve successive roller pairs with their coordinated baths are required in addition to the drying and crimping cylinders.

The start of the operation or the threading of the yarn is effected with slowly rotating rollers by the use of a temporary narrow, preferably, elastic belt located on the roller pair and rotated by the same. The yarns extruded from the spinnerets are attached to a projection of the rotating belt and guided around the roller pair the desired number of circuits; the yarn is then detached and placed on the next adjacent roller pair where the threading operation is repeated; hereafter the belts are taken off the rollers; they should preferably have a color contrasting to that of the yarn.

The invention and the method of performing the same will now be described in detail and with reference to the attached drawings showing a preferred embodiment thereof.

The continuous horizontal yarn spinning equipment forming the subject matter of my invention essentially comprises one long trough l of preferably rectangular cross section; this trough is divided by the partition walls 2 in successive compartments denoted with a, b, c, d, e and so forth in conformity with the number of individual processing baths or stages.

Vertically spaced roller pairs of the nonparallel type are coordinated to these. compart ments the roller pairs consisting of the upper rollers ,4, 4', 4'34", andso forth and the lower 7 rollers 3, 3, 3.", 3" and so forth, see Fig. 1. The rollers which are shown as solid bodies may be preferably made hollow to reduce their weight.

In the embodiment of the invention shown in the drawings the upper rollers are slightly inclined in a vertical plan relative to the lower rollers which are horizontal the angle of inclination being maintained within the above described limits; this relationship is schematically illustrated in Fig. 6 showing on an exaggerated scale the inclination of the upper roller 4 relative to the lower roller 3 and the upward travel of the individual yarn groups 38, 38', 39" in conformity with the number of the spinnerets and their customary accessories.

A frame structure composed of the longitudinal beams 5, vertical beams 8 of which only two are shown and connecting cross beams 'I, see Figs. 2 and 3, is provided to support the rollers and their driving means which latter mainly consist of one motor driven main shaft l and intermediary driving elements 1 l branching-off from the shaft and connected by link belts 2 with the lower rollers 3; driving motor including its customary speed reducer should be preferably placed at the spinneret end of the installation as a larger amount of power will be used to drive the viscose pumps, not shown, and the first roller pairs where the stretching of the yarns is accomplished. A

doctor 63 and a launder 14, see Fig. 2, is provided underneath each upper roller to take care of the surplus treating fluid. The traveling direction of the yarns is indicated by arrows, see 2. The viscose filaments leaving the filters 2! are in the customary manner extruded from the spinning jets 29 into the first'coagulation bath located in compartment a, Figs. 1 and 2. This bath may consist of a diluted sulphuric acid containing, for instance, sodium sulphate, zinc sulphate, ammonium sulphate and glucose in order to effect the coagulation of the extruded viscose filaments. The yarns 22 are hereafter passed into compartment 1) and there into 0 where the regeneration is completed. The baths 1) and c carry similar solutions but having a greater percentage of acid; compartment. (1 may carry wash water and the following compartments 6 and so forth carry the various treating, impregnating and finishing liquids; the yarns are then conducted over the dry ing cylinders 25 and eventually through crimping rollers 25 and collected on the cone 28 or similar yarn winding devices. The rollers run with their lower portions in contact with the various processing fluids; in this manner they take up the required amount of liquid.

Instead of rotating the lower rollers in direct contact with the treating fluids the device shown in Fig. 5 may be used where a small roller is kept in contact with the processing liquid and applies the same to the lower roller 3. The treating liquids may also be applied to the upper rollers by means of a spraying device, not shown in the drawings.

The yarns 22 resulting from the filaments 8 by coagulation in compartment u are carried onto the upper roller 4 of the non-parallel first roller pair 3, 4 which is coordinated with the regenerating bath b. The yarns pass over this roller pair 3, 4 in groups 30, 30, 30 and so forth in accordance with the number of the spinnerets, the groups consisting of 4 adjacent circuits as schematically illustrated in Fig. 6. The number of the spiral circuits within the individual groups may vary as before stated. Hereupon the yarns are conducted by suitable guiding devices such as guiding roller 32 see Fig. 2, onto the next non-parallel roller set 3, 4 located in compartment 0, see Fig. .1; these guiding devices are particularly useful if all inclined rollers are inclined in the same direction. This procedure is repeated throughout the various washing, processing and finishing baths whereupon the finally treated yarns leave the non-parallel roller bed, are conducted over the drier drums 24 and crimping rolls 25 and assembled on the cone 28 as finished yarns.

Various means of conducting the yarns over the roller pairs are illustrated in the drawings.

In conformity with Fig. 2 only the upper roller is tilted and this relationship is also illustrated in Fig. 6. The yarns will upwardly move on the tilted roller l and accordingly on the roller pair 3, t in groups composed of adjacent spiral circuits until they are taken off this roller pair and conducted to the same starting place on the next roller pair 3', 4 where the described travel of the yarn is repeated. In this manner the yarn is passed over the entire non-parallel roller bed.

In conformity with Fig. 4 the top rollers of the successive roller pairs are tilted in vertically opposite directions; the yarn groups accordingly travel over the adjacent roller pairs in longitudinally opposite directions and are thus passed from one to the next roller pair.

The level of the treating fluids in each compartment is kept as constant as possible. The partitions 2 separating the individual baths may be made removable, as shown in Fig. 1, in order to vary the mutual length of these baths; in this manner two adjacent compartments may be united into one single longer compartment. If adjacent compartments carry similar treating fluids they may be charged in conformity with the counter-current system as schematically indicated by the inlet and outflow tubes 33, 34 in compartments in and c of Fig. 1.

The level of the processing fluids in each compartmen is kept as constant as possible. If several baths of the same type are used, as, for instance, several regenerating or washing baths they might be operatively connected in conformity with the known counter-current principle whereby the liquids flow from one bath into the other bath in a direction opposite to the traveling direction of the yarn.

As the yarns do not dry out in passing from one to the other roller of each roller pair it results that complete regeneration, washing or other treatment can be effected during the passage of the yarns over the roller pairs with a replacement of the treating liquids by new liquid every time the yarn passes over the surface of the lower roller. A removal of used treating liquids is effected as the yarns pass around the upper roller by the previously mentioned doctor and launder equipment.

By varying the number of the yarn circuits in the individual roller groups the treatment may be widely controlled in conformity with special requirements.

The succession of the baths coordinated to a non-parallel roller pair may preferably be as follows:

1. A dilute acid bath to coagulate the filaments and to produce cellulose xanthate.

2. One or two baths carrying acid to form cellulose hydrate.

3. A water bath to remove the acid by washassaoeaev 4. A second water bath to complete the wash-'- ing; this second bath may have a small per-' centage of alkali added to complete the wash- 5. A desulfurizing bath in which the treating liquid will be a sulfur removing material, such as sodium sulfite or sodium sulfide.

6. A water bath to remove the desulfurizing chemicals from-the yarns.- 4

7. A bleaching containing, for instance, sodium hypochlorite.

8. A water bath to remove the bleaching chemicals.

9. A bath containing a sizing emulsion or a dye if it is desired to dye the yarn.

10. A water bath for the removal of excess size or dye.

11. An oil emulsion to bring the yarn into condition for use on the loom. When making tire cords, a latex emulsion may be used in replacement of the size or oil emulsion.

A non-parallel roller pair is coordinated to each bath in the manner shown in the drawing.

The above described equipment may be used with equal advantage for the production of the finest up to the heaviest yarns such as used for tire cords and staple fibers; the yarns may be combined at any place of the equipment and without interruption of the process.

The here described manufacturing method and equipment affords a most appropriate field of application for the manufacture of rayon tire cords.

The poor adhesion of rubber and latex containing liquids to rayon filaments, yarns and cords is a generally accepted fact in contradistinction to cotton cords whose projecting fine hairs greatly promote the coherence with the rubber. The viscose made yarn consisting of regenerated cellulose possesses a preponderance of a watery solution. There is strong indication that the cellulose is saturated with the liquid and that the surface of the cellulose yarn is a soft jelly which is only partly dissolved in the adjacent aqueous liquid contacting the yarn. These surface conditions of the liquid saturated and not previously dried rayon yarns result in a rapid and intensive absorption of the rubber liquid; this absorption is additionally improved by the previously described change of the shape of the yarns and movement of the latex emulsion during the passage of the yarn circuits over the roller pairs. Under these conditions the rubber precipitated from a dilute alkaline emulsion on the yarn thoroughly coats the surface of the yarn filaments and where the yarn is dried the tire cord is in the optimum condition for industrial use.

The rubber coating process may be modified and improved by an increase of the electric surface charge. This is accomplished by giving the yarn in the bath prior to the rubber impregnation a treatment with a solution of a cationic wetting agent or with a solution of an organic and preferably aromatic acid and then passing the thus treated yarn into a latex emulsion. The known method to increase the latex adherence to the wet yarns by surface roughening or the production of insoluble surface deposits, for instance, barium sulphate crystals may be used in combination with my process.

The performance of this invention is not restricted to the production of rayon yarn as artificial horsehair, artificial straw and similar cellulose materials may be produced in conformity with this invention by the described and shown equipment of which changes may be made within the scope of the appended claims.

What I claim is:

1. An apparatus for the continuous manufacture of rayon yarns comprising adjacent nozzles to produce a plurality of adjacently spaced cellulose yarns, a series of successive treating baths, a horizontal roller bed composed of successive pairs of vertically superposed smooth top and bottom rollers coordinated to said treating baths, each pair of rollers extending the entire width thereof, the roller axes of a pair of rollers being disposed in the same vertical plane and one of said rollers being tilted relatively to the other roller in such a manner that the distance between said roller axes increases in the advance direction of the yarns from one to the other end of the rollers.

2. In an apparatus according to claim 1, the degree of tilt corresponding to an angle of up to 18 minutes.

3. In an apparatus according to claim 1, doctors and launders being located in operative contact with the lower iace of the top rollers.

4. In an apparatus according to claim 1, a trough extending substantially through the length of the roller bed to accommodate the successive treating baths and the bottom rollers reaching in said baths with their lower portions, one main driving shaft located ad acent said trough and means including belts operatively connected to said main shaft to rotate the lower rollers only.

5. In an apparatus according to claim 1 a roller having a smaller diameter than the rollers of said roller pairs being located beneath the lower rollers and in contact therewith, the level of the processing baths being controlled to contact the lower face of said contacting roller.

6. In an apparatus according to claim 1 the top rollers of successive roller pairs being tilted in an opposite direction.

7. A method for the continuous manufacture of rayon yarns comprising extruding a viscose solution through adlacent nozzles into a coagulating bath to produce a plurality of ad acentiy spaced cellulose yarns, treating the said yarns upon emergence from said coagulating bath in a successive series or processing baths while conducting the same through a horizontal roller bed composed or successive vertically superposed smooth roller pairs coordinated to said baths and extending their entire width, the roller axes of each pair or roiiers being tiited relatively to each other in such a manner that the distance between said rolier axes increases in the advance direction or the yarns rroin one to the other roiier end, stretching the ad acent mdividuai yarns during their passage over the tilted roiier pairs in conformity with said distance increase, controiiing the surface level or the processing paths to remain beneath the horizontal center piane of the lower roller and drying the formed yarns.

8. In a method according to claim 7 stretching the yarns during their travel through said roller bed by an increase of the rotational speed of the second roller pairs relatively to the first pair.

9. In a method according to claim '7, shrinking the yarns by a reduction of the rotational speed of the third roller pair of said roller bed relative to the rotational speed of the second roller pair.

10. In a method according to claim 7 conduct- 11' ing the bath liquids in a counter-current direc- Number tion to the traveling direction of the yarns. 2,146,747 RALPH H. MCKEE. 2,309,072 2,334,325 References Cited in the file of this patent 5 2346596 UNITED STATES PATENTS Number Name Date Number 2,042,437 Taylor May 26, 1936 483,496 2,108,285 Forrest Feb. 15, 1938 10 Name Date Kline et a1. Feb. 14, 1939 Burkholder Jan. 19, 1943 Heim Nov. 16, 1943 Moritz et a1 Apr. 18, 1944 FOREIGN PATENTS Country Date Great Britain Apr. 21, 1938 

